1. Field of the Invention
The present invention is directed to a coordinate detecting device and a coordinate detecting method.
2. Description of the Related Art
Touch panels are an example of input devices for computer systems. A touch panel is mounted on a display to detect a coordinate position on the display and obtain a detection signal corresponding to the coordinate position. The panel allows a direct input and enables a user to have an easy and intuitive input.
Various types of touch panels have been proposed, including resistive touch panels, optical touch panels and capacitively-coupled touch panels. Among them, resistive touch panels having a simple configuration and control system are in widespread use. Low resistive touch panels include four-wire, five-wire and eight-wire touch panels, for example, the difference of which comes in how electrodes are arranged on a resistive film.
Compared to four-wire and eight-wire touch panels, five-wire touch panels are free from edge sliding, which is a shortcoming of the four-wire and eight-wire touch panels. This is because, in the five-wire touch panels, a conductive film of the upper substrate which is disposed on the operation surface is used only for reading an electric potential. Accordingly, the five-wire touch panels are used in harsh usage environments and markets requiring touch-panels with long-life durability.
FIG. 12 shows a structural diagram of a five-wire resistive touch panel. A five-wire resistive touch panel 1 includes an upper substrate 11 and a lower substrate 12. In the lower substrate 12, a transparent resistive film 22 is formed over the entire surface of a glass substrate 21, and X-axis coordinate detecting electrodes 23 and 24 and Y-axis coordinate detecting electrodes 25 and 26 are disposed on the transparent resistive film 22. In the upper substrate 11, a transparent resistive film 32 is formed on a film substrate 31, and a coordinate detecting electrode 33 is disposed on top of the transparent resistive film 32.
When a voltage is applied to the X-axis coordinate detecting electrodes 23 and 24, an electric potential distribution is obtained in the X-axis direction in the transparent resistance film 22 of the lower substrate 12. At this point, the electric potential in the transparent resistive film 22 of the lower substrate 12 is detected, thereby detecting an X coordinate of a contact point where the upper substrate 11 comes in contact with the lower substrate 12. Subsequently, by applying a voltage to the Y-axis coordinate detecting electrodes 25 and 26, an electric potential distribution is obtained in the Y-axis direction in the transparent resistive film 22 of the lower substrate 12. At this point, the electric potential in the transparent resistive film 22 of the lower substrate 12 is detected, thereby detecting a Y coordinate of the contact point.
Patent Document 1 discloses such a coordinate detecting device having improved precision in detecting a coordinate position.
[Patent Document 1] Japanese Laid-open Patent Application Publication No. H10-83251
The coordinate detecting device of Patent Document 1 is able to perform precise detection when contact is made at one point; however, if contact is made at two points, the coordinate detecting device is not able to distinguish between the two points, and cannot therefore detect the two contact points at all. Although methods for detecting two contact points have been proposed, many of the cases solve the problem by dividing the transparent resistive film. Dividing the transparent resistive film causes a divisional boundary to stand out, resulting in a reduction in aesthetic appearance. Such aesthetic appearance degradation could be fatal for touch panels and other display panels, and therefore, there is a demand a method for detecting two contact points without dividing the transparent resistive film.